Actually, we've figured out the real culprit is when someone is downloading the pwad from the server via the odamex client. The server will disappear (or sometimes show up as BAD PACKET DATA) when a client is downloading.

there is bug in Odamex: when client connect and start to download wad from server, 'numclient' cvar is increased but server doesn't send to launcher information about this client, so launcher tried to read data behind the packet

i dont know how to report this error to odamex team: forum doesnt work and bug tracker is too tangled imho